The invention relates to an apparatus for weighing in a bird, which hangs from a shackle of known weight carried by a continuously moving overhead conveyor.
In the poultry processing industry it is common practice to weigh the processed birds as they are transported by an overhead conveyor, in order to devide the birds in weight classes, each with a weight range of about 50 gram. After the weight of the birds is established, they are automatically released from the conveyor shackles as they pass a series of receiving bins corresponding with the different weight classes. Apart from grading or sizing the birds it is also desirable to weigh the birds during the different stages of processing in order to establish and control yield losses and/or water pick-up.
In a known apparatus for weighing birds each conveyor shackle is provided with a special pivotable link with a pair of rollers, which when the shackle passes a weighing station are guided onto a pair of rails spaced below the conveyor track. The first part of these rails slopes upwards, so that the link gradually pivots backwards and the full weight of the bird and the shackle becomes solely supported by the rollers. The rollers then pass a weighing bridge fitted into a gap in the rails and supported by a load cell or another weighing element, which measures the total weight supported by the rollers as they pass the weighing bridge. The length of the weighing bridge is limited to less than the distance between subsequent shackles, which in practice would be 6 inches or about 15 cm.
The main problem with an apparatus of this kind is that due to friction in the rollers and friction between the rollers and the rails, the conveyor still has to apply a substantial force on the link in order to drag the shackle over the bridge. Since these frictions vary from shackle to shackle and with the conveyor speed, this dragging force is not a constant and therefor has a detrimental influence on the accuracy of the measurements, especially when after some time the rollers are worn and when conveyor speeds of 6000-12000 birds per hour are used, which is not exceptional in practice.
Another problem is that an apparatus of the known type can only be used in combination with special shackles with rollers. Apart from being expensive these shackles can not be used during certain stages of the total process. In the defeathering department such shackles would be damaged by the defeathering machines and weighing the birds would be impossible.